1. Field of the Invention
The present invention relates to a dispensing gun, and more particularly to a dispensing gun including a pressure relieving device for suitably and effectively dispensing viscous materials, such as thick fluid or liquid, pasty materials, or mastic caulking materials, and for relieving the pressure of the viscous materials or the mastic caulking materials within the cartridge, and for preventing the viscous materials or the mastic caulking materials from moving out of the cartridge continuously after the required squeezing or dispensing operation.
2. Description of the Prior Art
Various kinds of typical dispensing guns have been developed and provided for dispensing various kinds of viscous materials, such as thick fluid or liquid, pasty materials, or mastic caulking materials which are retained in a cartridge that includes a discharge nozzle, and that includes an open end, and that includes a cup-shaped piston slidably received in the cartridge.
For example, U.S. Pat. No. 5,156,305 to Eyre, U.S. Pat. No. 5,381,931 to Chang, and U.S. Pat. No. 5,626,263 to Lii disclose several of the typical dispensing guns each comprising a rod slidably received in a supporting member and including a rack formed or provided therein, and a pair of pawls biased to engage with the rack with spring members for moving the rod forward step by step, and for forcing the piston to move forward and thus for forcing or squeezing the viscous materials or fluid out of the cartridge.
The pawls may only be used to force and to push the rod forward step by step, such that the viscous materials or fluid may be pressurized by the piston, and may be caused to move out of the cartridge continuously. Much of the viscous materials or fluid may thus be forced out of the cartridge continuously, and may be wasted and may not be used.
When the rod is moved rearwardly or backwardly by a release plate and an actuating handle or hand grip, a hollow compartment may be formed in the front end of the cartridge, next time, when the rod is forced to move forward by the actuating plate again, the piston may not be used to move or force any viscous materials or fluid out of the cartridge, the air received in the hollow compartment formed in the front end of the cartridge should be forced out of the cartridge before the viscous materials may be pressurized again by the piston. The actuating plate is thus required to be actuated many times before the required amount of mastic caulking materials or fluid may be forced or squeezed out of the cartridge.
However, when the hollow compartment is formed in the front end of the cartridge and when the rod is moved rearwardly or backwardly by the release plate, the air in the outer environment may be drawn into the cartridge, such that the mastic caulking materials may be easily hardened by the air. Furthermore, when the front end of the dispensing gun is directed upwardly or downwardly, the bush may not suitably engage with the release plate, and the rod thus may not be actuated or moved rearward by the release plate, such that the viscous materials may still be caused to move out of the cartridge continuously.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional mechanisms for the dispensing guns.